摘要:

The effect of organic particle mass loading from 1 to >= 100 mu g m(-3) on the cloud condensation nuclei (CCN) properties of mixed organic-sulfate particles was investigated in the Harvard Environmental Chamber. Mixed particles were produced by the condensation of organic molecules onto ammonium sulfate particles during the dark ozonolysis of alpha-pinene. A continuous-flow mode of the chamber provided stable conditions over long time periods, allowing for signal integration and hence increased measurement precision at low organic mass loadings representative of atmospheric conditions. CCN activity was measured at eight mass loadings for 80- and 100-nm particles grown on 50-nm sulfate seeds. A two-component (organic/sulfate) Kohler model, which included the particle heterogeneity arising from DMA size selection and from organic volume fraction for the selected 80- and 100-nm particles, was used to predict CCN activity. For organic mass loadings of 2.9 mu g m(-3) and greater, the observed activation curves were well predicted using a single set of physicochemical parameters for the organic component. For mass loadings of 1.74 mu g m(-3) and less, the observed CCN activity increased beyond predicted values using the same parameters, implying changed physicochemical properties of the organic component. A sensitivity analysis suggests that a drop in surface tension must be invoked to explain quantitatively the CCN observations at low SOA particle mass loadings. Other factors, such as decreased molecular weight, increased density, or increased van't Hoff factor, can contribute to the explanation but are quantitatively insufficient as the full explanation.

附注:

ISI Document Delivery No.: 447KJTimes Cited: 10Cited Reference Count: 45King, S. M. Rosenoern, T. Shilling, J. E. Chen, Q. Martin, S. T.Office of Science (BES), US Department of Energy [DE-FG02-08ER64529]; National Science Foundation [ATM-0513463]; EPA STAR fellowship program ; Danish Agency for Science Technology and Innovation [272-06-0318]; NASA Earth and Space Science FellowshipThis material is based upon work supported by the Office of Science (BES), US Department of Energy, Grant No. DE-FG02-08ER64529 and by the National Science Foundation under Grant No. ATM-0513463. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the Department of Energy or the National Science Foundation. SMK acknowledges support from the EPA STAR fellowship program. TR acknowledges support from the Danish Agency for Science Technology and Innovation under Grant No. 272-06-0318. QC acknowledges support from the NASA Earth and Space Science Fellowship.Copernicus publicationsKathlenburg-lindau